How does the brain change with experience? Once the brain is mature, can it be rewired by growth of new synapses and loss of older ones? Classic studies measuring spine densities or synapse numbers have relied on post-mortem techniques which do not allow direct observation of spine growth and loss. Recently, 2-photon microscopy in fluorescent protein transgenic animals has made it possible to follow dendrites and spines over weeks to months of an animal's life. The aim of the project will be to describe the long-term effect of sensory experience changes on dendrite and spine persistence in layer V and layer I I/I 11 neurons of the barrel cortex. Receptive field plasticity has been observed in deprived barrel columns where responses to deprived whiskers become depressed within days and responses to adjacent spared whiskers are enhanced 1-3 weeks later. It is not known if either process involves the formation or loss of synapses. Using long-term in vivo imaging and electron microscopy in wild-type and alphaCamKIIT286A (receptive field plasticity impaired) mice, we will document the loss and formation of synapses that occur normally and 1- 3 weeks after chessboard whisker deprivation.